Hydrocarbon producing wells are often stimulated by hydraulic fracturing treatments. In hydraulic fracturing, a viscous gelled fracturing fluid which also functions as a carrier fluid is pumped into a subterranean zone to be fractured at a rate and pressure such that one or more fractures are formed in the zone. Proppant particles, e.g., graded sand, for propping the fractures open are suspended in the fracturing fluid. After forming the fracture(s), a viscosity breaker is used to cause the fracturing fluid to revert to a thin fluid, i.e., “break” the viscosity, after which the fracturing fluid can be returned to the surface. Once the viscosity of the fracturing fluid is broken, the proppant particles are deposited in the fractures and function to prevent the fractures from closing so that conductive channels are formed through which fluids can readily flow.
In order to prevent the subsequent flow-back of the proppant particles as well as loose or incompetent fines with fluids produced from the subterranean zone, the proppant particles have heretofore been coated with a hardenable resin composition which is caused to harden and consolidate the proppant particles in the zone. As a general rule, consolidation requires that closure stress must be applied to the proppant grains to insure resin coated particle-to-particle contact. However, many hydraulic fractures do not completely close during the first 24 hours after fracturing treatments, especially in low-permeability formations. This results in poor consolidation. Poor consolidation allows proppant particles and formation fines to flow-back with produced formation fluids. The flow-back of the proppant particles and formation fines is very detrimental in that it erodes metal goods, plugs piping and vessels and causes damage to valves, instruments and other production equipment.
The resin coating of a pre-coated resin particle is already partially cured (hardened) to provide for storage and handling, so only a portion of the resin is available for hardening in the subterranean zone and thereby contributing to the ultimate consolidation strength. As the resin coated proppant is deposited in the fracture(s) and exposed to higher formation temperatures, the resin curing process is re-initiated. The more the resin coating cures or hardens before the resin coated proppant particles are brought into contact with each other, the lower the consolidation strength that will be developed.
Difficulty in achieving this contact is due in part to the gelled carrier fluid that forms a film of gelled carrier fluid on the surface of the resin coated proppant particles. This film significantly hinders contact between the resin coated proppant particles, and thus reduces the consolidation strength that can develop.
Thus, there are needs for improved methods of consolidating proppant particles in subterranean fractures whereby permeable packs of consolidated proppant particles are formed.